Buddhi
Buddhi refers to the intellectual faculty and the power to "form and retain concepts, reason, discern, judge, comprehend, understand".
Etymology
Buddhi is derived from the Vedic Sanskrit root Budh, which literally means "to wake, be awake, observe, heed, attend, learn, become aware of, to know, be conscious again". The term appears extensively in Rigveda and other Vedic literature. Buddhi means, states Monier Williams, the power to "form, retain concepts; intelligence, reason, intellect, mind", the intellectual faculty and the ability to "discern, judge, comprehend, understand" something.Buddhi is a feminine Sanskrit noun derived from *budh, to be awake, to understand, to know. The same root is the basis for the more familiar masculine form Buddha and the abstract noun bodhi.
Buddhi contrasts from manas which means "mind", and ahamkara which means "ego, I-sense in egotism".
Usage
In Sankhya and yogic philosophy both the mind and the ego are forms in the realm of nature that have emerged into materiality as a function of the three gunas through a misapprehension of purusha . Discriminative in nature, buddhi is that which is able to discern truth from falsehood and thereby to make wisdom possible.The Sānkhya-Yoga view
According to the Sānkhya-Yoga view, buddhi is in essence unconscious, and as such, cannot be an object of its own consciousness. This means that it can neither apprehend an object nor manifest itself.In the Yoga Sutra, it is explained that the buddhi cannot illuminate itself, since it itself is the object of sight, "na tat svabhāsam draśyatvāt".
In the Samkhyakarika, buddhi, originally referred to as mahat, is the fundamental entity that emerges during Prakrti's cosmic self-transformation. It has the sense of knowledge, and is synonymous with words like thought, idea, wisdom, and insight. Buddhi is characterized by its function as judgment, as it not only identifies the nature of things but also determines the best course of action. From buddhi arises ahamkara, the "I-maker", which begins the cosmic differentiation, producing inner sensation through its transformed aspect and external perceptions through its elemental aspect, laying the foundation for subjectivity, objectivity, and self-awareness.